**Core Concept**
Congenital Hypertrophic Pyloric Stenosis (CHPS) is a condition characterized by thickening of the pyloric muscle, leading to gastric outlet obstruction in infants. The pathophysiology involves abnormal hypertrophy of the pyloric muscle, which can be visualized and diagnosed using ultrasound.

**Why the Correct Answer is Right**
The correct ultrasound features of CHPS include:
* Thickened pyloric muscle (>4 mm) due to hyperplasia of the smooth muscle cells.
* Hypertrophied pyloric muscle with a lengthened pyloric canal (>16 mm).
* Pyloric channel lengthening with a narrowed pyloric lumen.
* Increased pyloric muscle thickness ratio (usually >3-4 mm).

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertrophied pyloric muscle is a characteristic feature of CHPS, so this option is incorrect.
**Option B:** Increased pyloric muscle thickness ratio is a common finding in CHPS, making this option incorrect.
**Option C:** Thickened pyloric muscle is a hallmark of CHPS, so this option is also incorrect.

**Clinical Pearl / High-Yield Fact**
A classic mnemonic to remember the key ultrasound features of CHPS is "THICK": Thickened pyloric muscle, Hypertrophied pyloric muscle, Increased pyloric muscle thickness ratio, and Key features of pyloric stenosis (channel lengthening and narrowing).

**Correct Answer: C. Normal pyloric muscle thickness.**